This invention relates to a method and a system that controls the supply of nitrogen to a gas volume in electrical power handling equipment, such as electrical transformers, and related equipment, such as load tap changers, control boxes and the like.
An electrical power handling equipment, such as a transformer, includes a tank filed with oil in which the power handling devices or coils are disposed.
The gas volume or ullage above the oil in the tank is generally filled with nitrogen to avoid an air atmosphere that contaminates the oil due to oxidation and/or moisture absorption. The nitrogen has generally been supplied from high pressure cylinders regulated down to an appropriate pressure. The pressure in the ullage is controlled in a range of 0.5 psi to 5 psi. The use of nitrogen cylinders has some drawbacks. The nitrogen cylinders need to be replaced on a regular basis, since the ullage is changing due to changing temperature of the oil. Leaks sometimes arise in the cylinder that cause an earlier replacement. The cylinders are heavy and can cause injuries during the replacement process. The wide pressure range in the ullage can lead to substantial nitrogen bubbling in the oil due to pressure changes caused by weather conditions or other influences. If the bubbling occurs in the region of active contacts, arcing can occur. Also, cylinder replacement is a recurring cost.
Nitrogen generators derive nitrogen from a supply of compressed air. Nitrogen generators have a number of uses in manufacturing operations within the environment of a manufacturing plant as described in an article entitled xe2x80x9cAvoiding the Hassles of Liquid Nitrogenxe2x80x9d, Chemical Engineering, July, 1993. These uses include keeping components dry, eliminating sparks during welding and providing a safety curtain at the entrance and exit of a hydrogen furnace. However, none of these applications involve an outdoor environment or a nitrogen interface with a volume of oil.
Accordingly, there is a need to supply nitrogen to electrical power handling equipment in an outdoor environment that is cost effective and eliminates the use of high-pressure cylinders.
The method and system of the present invention satisfy the aforementioned need by supplying nitrogen to the ullage above an oil volume in an electrical power handling equipment, such as a power transformer. The pressure in the ullage is controlled in a range of about 0.5 psi to about 2.0 psi. This substantially minimizes nitrogen bubbling in the oil due to changes in pressure as might occur due to changes in loading or weather. The nitrogen is derived by a nitrogen generator from a supply of compressed air.
In some embodiments of the invention, the nitrogen is supplied at a relatively low pressure during a normal operating interval and at a relatively high pressure during a start up interval. The low-pressure nitrogen is obtained with a nitrogen generator that derives the nitrogen from the compressed air supply. The high-pressure nitrogen is obtained from a high-pressure source such as a high-pressure cylinder.
In other embodiments, the ambient temperature of the power handling equipment is regulated in a range from a low temperature to a high temperature. This regulation is especially advantageous in power substations that house the electrical power handling equipment.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract included below, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.